1. Field of the Invention
This invention relates to improvements in electronic power supply circuits, and, more particularly, to improvements in power supply inverter circuits for powering loads such as AC motors and the like which require regulated voltages for maintenance of a particular operating state or nominal condition.
2. Description of the Prior Art
In many instances, it is desired to provide an AC voltage which is controlled to maintain a certain operating condition or state of a load. For example, in the operation of AC motors, particularly in environments such as aircraft gyros and the like, maintaining a constant gyro rpm is of particular importance. The maintenance of an aircraft gyroscope motor at a constant operating rpm is difficult, in part, because of the permissible voltage variations which are encountered. The present Federal Aviation Administration standards permit a variation in voltage of plus or minus 15 percent volts DC of the aircraft voltage supply; and gyros, such as may be employed for aviation instruments, should be maintained at a particular rpm for proper service.
Presently, aircraft gyros, for instance, are designed to perform properly at the low voltage range which may be encountered. Consequently, with a conventional power supply, all voltage which is applied higher than the permissible low voltage is wasted during the normal operating mode. At these higher voltages, extra current is applied to the gyro motor which may manifest itself in the form of additional heat which reduces the bearing life by evaporating the bearing lubricants, resulting in a reduction of the lifespan of the motor. Additionally, these voltage changes may affect the rpm of the gyro. The current and voltage relationship is linear, unless a regulator is provided, and, in that event, the regulator regulates the voltage so that further input voltage increases do not result in further increases in output voltage or current. Voltage regulators must be set at a low voltage within the operating range, so that as the input voltage is increased, the voltage applied to the gyro motor stays constant. This results in gyro motors requiring longer periods of time to attain rated operating speed, because the torque is limited due to the lack of amplitude of available voltage. Additionally, the regulator itself imposes an additional load on the power supply which manifests itself in the form of waste heat.